1. Field of the Invention
The invention relates to a door lock including spring bolt and dead bolt with all structural parts made from thermoplastic synthetic resin and with the follower body being an injection molded structure installed without bias and exerting spring action by virtue of the resilience inherent in the material when designed in a specific way.
2. Description of the Prior Art
In the known door locks the follower body is mostly made of metal and installed in the door locks in a wide variety of embodiments. Such follower bodies, in the pertinent field simply termed follower, are held in a predetermined desired inoperative position by various types of springs. On principle, all the required springs are installed with bias in the door lock.
In the staple door lock which is sold for a relatively low price a spiral spring made from normal sheet steel and having an extended leg portion is used. By way of a connecting member the free end of the spring leg is biased against the follower hook.
The selling price dictates the quality of such door locks. Particularly the materials used for the follower and for the spring bolt spring and tumbler spring determine the service life of the door lock. Even locks of higher quality do not guarantee for the durability of the springs. If they do not break prematurely the springs slacken due to fatigue whereupon the bias decreases with the consequence that the door handle is no longer held in the desired position.
All door lock springs have a predetermined function. Thus, the spring bolt spring has the task of always holding the spring bolt in closing position. The force of said spring is dimensioned such that said force can be easily overcome by the inclined surface of the spring bolt head without actuation of the door handle. This happens when the door is merely pulled shut.
In addition to the aforementioned springs a tumbler spring is required which secures the dead bolt prior to and after locking.
To cut costs the spring bolt spring and the tumbler spring have been designed as a combination spring. This implies that such a spring with a free leg thereof urges against the spring bolt head at a suitable location thereof and simultaneously urges against the tumbler, a solution that is satisfactory only under the aspect of selling prices.
Despite all simplifications and combinations which highly reduce the quality of the door lock the manufacturing costs are still very high and the final product is relatively expensive while the quality nevertheless is hardly satisfactory.
Attempts to overcome the indicated shortcomings resulted in various constructions while the problem proper is still unsolved. Thus, French Patent No. 2,222,875 discloses a door lock construction using plastic parts. The functional parts, when made of plastic, may be subject to fatigue which ultimately will render the lock useless.